Paulo Freire´s Contributions to the Research and Critical Reading
6. Conclusiones
One of the major characteristics of the local irrigation water is the high concentration of sodium. Because the local distribution water source is a deep groundwater well containing high bicarbonate-alkalinity and high sodium, soil irrigated with this water has a high sodium
saturation. When the sodium has no more cation exchange sites available, the excess sodium leaches into the shallow groundwater and leaves a variable irrigation water “signature” in the surface water streams. Though in less abundance, the other cations, namely potassium,
magnesium and calcium, serve an important purpose in both soil and water systems as nutrients necessary for plant and microbial growth.
0 2 4 6 8 10 12
O rt h o p h o sp h at e ( m g /L)
Sample Site
Summer Fall Winter Spring
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3.1.5.1. Low Flow Conditions
During low flow conditions, there were several differences in sodium concentrations among the creeks. Wolfpen was significantly higher in sodium than all other watersheds besides Carter 5, probably from its high amount of irrigation water from the Texas A&M golf course (Figure 15). Carter 4 and 5 were higher than Briar 2, Burton 4, Carter 1 and Carter 3, all sites closer to the top of their respective watersheds that have not perhaps collected as much of the
tap/irrigation signature. Carter 3, with the lowest amount, was the most rural site and thus the least impacted by the sodic tap water.
As a major nutrient and electrolyte for humans, potassium has a high turnover rate in urban environments and is often seen to increase in wastewater. True to form, potassium
concentrations were significantly higher in Carter 4 and 5 than in Wolfpen and in Burton 1, 3 and 4 (Figure 16). Carter 5 was significantly higher than all Burton and Briar sample sites as well as Hudson and Wolfpen Creeks.
Low flow magnesium concentrations, unlike nitrate, orthophosphate, sodium and potassium concentrations, showed Carter 4 with significantly lower concentrations than Carter 3, Burton 3 and Bee Creek (Figure 17). On the other end of the scale, Bee Creek was higher than all other sites besides Burton 3, which was higher than all remaining sites besides Carter 3.
Calcium concentrations were significantly higher in Bee Creek at 20.4 mg/L than in Burton 2 at 9.4 mg/L, but no other differences among the creeks were observed (Table 14).
Figure 15. Mean annual sodium concentrations at low flow. Error bars are standard error of the mean. Different letters indicate significant difference at p ≤ 0.05.
Figure 16. Mean annual potassium concentrations at low flow. Different letters indicate significant difference at p ≤ 0.05.
0 50 100 150 200 250
Mean Annual Sodium (mg/L)
Sample Site
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00
Bee
Potassium at Low Flow (mg/L)
Sample Site
47
Figure 17. Mean annual magnesium concentrations at low flow. Error bars are standard error of the mean. Different letters indicate significant difference at p ≤ 0.05.
Table 14. Mean annual calcium concentrations during low flow. Different letters signify a significant difference.
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
Bee
Magnesium at Low Flow (mg/L)
Sample Site
3.1.5.2. High Flow Conditions
During high flow conditions, cations exhibited a diluted effect from the greater quantity of flowing water added to base flow concentrations. Wider standard error values from the varying precipitation amounts, intensities and intervals between precipitation and sampling generally decreased the significant differences among the sample sites.
For sodium during high flow conditions, Wolfpen Creek maintained the highest
concentration and was still significantly higher than the Burton 1, 2, and 5; the Briar sites; and the upper Carter sites (Figure 18). Carter 4 and 5, both statistically similar to Wolfpen, were also higher than the upper Carter sites and Briar 2.
Potassium concentrations were higher in Carter 4 and 5 than in Briar 2; Burton 1, 2, 4 and 5;
Carter 2 and Wolfpen (Figure 19). In addition, Carter 4 was significantly higher than Burton 3 and Hudson Creeks.
High flow magnesium concentrations remained greatest in Bee Creek, but were not significantly greater than Burton 3, the upper Carter sites, Carter 5 and Wolfpen (Figure 20).
Bee Creek did have significantly more magnesium than both Briar sites; Burton 1, 2, 4 and 5;
Carter 4 and Hudson. Burton 3 and Carter 5 were significantly higher than Briar 2, Burton 1, Burton 2 and Carter 4.
There were no significant differences among the creeks from high flow calcium
concentrations. The mean annual concentrations ranged from 10.17 mg/L in Hudson Creek to 15.64 mg/L in Burton 3 (Table 15).
49
Figure 18. Mean annual sodium concentrations at high flow. Different letters indicate significant difference at p ≤ 0.05.
Figure 19. Mean annual potassium concentrations at high flow. Different letters indicate significant difference at p ≤ 0.05.
0 50 100 150 200
Sodium at High Flow (mg/L)
Sample Site
Potassium at High Flow (mg/L)
Sample Site
Figure 20. Mean annual magnesium concentrations at high flow. Different letters indicate significant difference at p ≤ 0.05.
Table 15. Mean annual calcium concentrations during high flow. Equivalent letters indicate no significant difference.
Site Name N Mean Std Dev Std
Magnesium at High Flow (mg/L)
Sample Site
51
3.1.5.3. All Flow Conditions
Mean annual cation concentrations showed similar patterns to high and low flow conditions.
Sodium once again showed the highest concentrations in Wolfpen, followed by Carter 5 and Carter 4 (Figure 21). Burton 3 and Hudson also had higher concentrations of sodium than did Briar 2, Carter 1 and Carter 3.
Potassium concentrations in all flow conditions were significantly higher at Carter 4 and 5 than at the other sites, with the exceptions of Carter 2, Carter 3 and Bee (Figure 22).
Concentrations of magnesium during all flow were greatest in Bee Creek and Burton 3 (Figure 23). Magnesium concentrations in Carter 3 were significantly higher than Briar 1, Burton 1, Burton 4 and Carter 4. Carter 4 was the lowest, with a mean significantly lower than Carter 2, Carter 3, Burton 3 and Bee Creek.
Mean annual calcium concentrations were significantly greater in Bee Creek than in Burton 2 and Carter 4, but no other significant differences were found (Table 16).
3.1.5.4. Seasonal Variation
Even in summer, Wolfpen maintained a higher sodium level than Carter 3. Fall sodium concentrations were higher in Wolfpen than all other sites except Carter 5. Carter 5 was higher than Briar 2, Burton 5, Carter 1 and Carter 3; Carter 4 was also higher than Carter 3. In winter, Carter 4, Carter 5 and Wolfpen were higher than Carter 3, Carter 1 and Briar 2. In addition, Carter 5 was higher than Carter 2; Burton 1, 2, 4 and 5; and Briar 1; while Wolfpen was higher than these plus Hudson and Bee Creeks. In spring, Carter 4, Carter 5 and Wolfpen were higher than Carter 3 and Briar 2, while Carter 4 was also higher than Carter 1 and Wolfpen was higher
than Carter 1 and Burton 1, 2, 4 and 5. Carter 3 mean sodium concentration varied little seasonally, from 30.2 mg/L in spring to 37.6 mg/L in the fall.
Potassium was higher in Carter 4 and 5 than in Wolfpen during spring. Spring
concentrations in Carter 5 were also higher than all the Burton sites and the upper Carter sites (1-3). In summer there was no significant difference among any of the sample sites. In winter, Carter 5 was higher than the other sites except for Carter 3 and 4, and those two sites were higher than Wolfpen and Burton 4. Fall potassium concentrations were significantly higher in Carter 5 than Hudson and Burton 1; Carter 3 was also higher than Burton 1.
Magnesium showed no significant difference among the creeks during the spring. In summer, Bee Creek was higher than the other sites except for Burton 3, Burton 5 and the upper Carter sites, but no other differences were observed. In the fall, Bee was higher than all the others except Carter 2, Carter 3 and Burton 3. Fall Burton 3 concentrations were higher than in
Figure 21. Mean annual sodium concentrations for all flow. Error bars are standard error of the mean. Different letters indicate significant difference at p ≤ 0.05.
0 50 100 150 200 250
Mean Annual Sodium (mg/L)
Sample Site
53
Figure 22. Mean annual potassium concentrations for all flow. Error bars are standard error of the mean. Different letters indicate significant difference at p ≤ 0.05.
Figure 23. Mean annual magnesium concentrations for all flow. Error bars are standard error of the mean. Different letters indicate significant difference at p ≤ 0.05.
0 1 2 3 4 5 6 7 8
Mean Annual Potassium (mg/L)
Sample Site
Mean Annual Magnesium (mg/L)
Sample Site
Table 16. Mean annual calcium concentrations for all flow. Equivalent letters indicate no significant difference at the p ≤ 0.05 level.
Site Name N Mean Std Dev Std Error Minimum Maximum
Bee 10 a14.79 6.25 1.98 3.61 24.67
Briar 1 10 a11.75 4.18 1.32 5.35 17.46
Briar 2 10 a12.79 4.84 1.53 5.59 18.63
Burton 1 10 a10.68 3.50 1.11 4.75 15.38
Burton 2 10 a11.00 3.52 1.11 5.91 16.91
Burton 3 10 a15.64 5.68 1.80 8.26 23.69
Burton 4 10 a13.33 4.43 1.40 7.88 20.56
Burton 5 10 a13.23 2.37 0.75 7.83 15.45
Carter 1 9 a12.73 4.25 1.42 8.24 22.15
Carter 2 9 a12.39 5.88 1.96 5.08 23.46
Carter 3 9 a14.57 3.30 1.10 7.93 18.89
Carter 4 10 a10.90 3.51 1.11 6.01 14.95
Carter 5 9 a12.09 2.57 0.86 7.62 15.16
Hudson 10 a10.17 4.94 1.56 2.59 20.00
Wolfpen 9 a10.67 2.98 0.99 6.55 15.28
Carter 4, Carter 5, Hudson, Burton 1, Burton 4 and the Briar sites, while Carter 3 was higher than Carter 4, Burton 1, Briar 1 and Hudson. Bee and Burton 3 were also highest among the sites in winter, while Carter 2 and 3 were only significantly higher than Carter 4.
Calcium concentrations in spring and summer showed no significant difference. In the fall, Carter 3 was higher in calcium than Briar 1, Burton 1 and 2, Carter 2 and Hudson. Bee Creek had the second highest fall mean value, but was not significantly different from any of the sites.
Winter calcium concentrations were greater in Bee Creek than in Carter 4.
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3.1.6. Anions: Chloride, Fluoride, Bromide and Sulfate 3.1.6.1. Low Flow Conditions
The previous section reported concentrations of cations, which are attracted to the negatively charged cation exchange sites on the surface of soil particles. Anions, on the other hand, do not attach very strongly to soil or particulate matter because of their negative charge, and are often observed in leachate water.
Under low flow conditions, chloride concentrations were highly variable among creeks.
Chloride in Burton 3 exceeded that in Carter 1, Carter 3 and Briar 2 (Figure 24), all sites close to the top of their respective subcatchments with the lowest chloride concentrations. In addition, Carter 5 was higher than Burton 4, Burton 5 and Hudson, and Carter 4 was higher than these three plus Carter 2. There was no significant accumulation from Carter 4 to Carter 5, possibly because the wastewater treatment plant upstream of Carter 5 uses UV-radiation for disinfection rather than an additional amount of chloride. As the site with the greatest chloride
concentration, Wolfpen Creek was significantly higher than in Hudson; the upper Carter sites (Carter 1-3); both Briar sites; and Burton 1, 2, 4 and 5.
Figure 24. Mean annual chloride concentrations at low flow. Error bars are standard error of the mean. Different letters indicate significant difference at p ≤ 0.05.
Fluoride concentrations during low flow were highest in Carter 4 and 5 downstream of wastewater treatment plants (Figure 25). Hudson Creek was next highest, with higher
concentrations than the upper Burton sites (3-5), upper Carter sites (1-3), and Briar 2. Wolfpen was also higher in fluoride than Carter 3 and Briar 2.
0 20 40 60 80 100
Mean Annual Chloride (mg/L)
Sample Site
57
Figure 25. Mean annual fluoride concentrations at low flow. Different letters indicate significant difference at p ≤ 0.05.
Unlike the low flow fluoride stream concentrations, bromide was higher in Wolfpen than in any other watershed sampled (Figure 26). Burton 5 was also higher than Briar 2 and Carter 3, possibly the effect of industry in the Burton 5 drainage basin. There was no significant difference between sites below wastewater treatment plants and most other urban watersheds.
Low flow sulfate concentrations were also highly variable. Bee creek sulfate was greater than in every other site besides Wolfpen (Figure 27). Hudson and Burton 3 were significantly higher than Briar 1 and 2, Burton 4 and the upper Carter sites. Carter 5 and Burton 5 followed, with higher concentrations than the Briar sites, Burton 4 and Carter 1 and 3. Carter 4 was higher than Briar 2, Burton 4 and Carter 1 and 3, while Burton 1 was higher than Briar 2 only.
0 0.2 0.4 0.6 0.8 1 1.2
Mean Annual Fluoride (mg/L)
Sample Site
Figure 26. Mean annual bromide concentrations at low flow. Error bars are standard error of the mean. Different letters indicate significant difference at p ≤ 0.05.
Figure 27. Mean annual sulfate concentrations at low flow. Error bars are standard error of the mean. Different letters indicate significant difference at p ≤ 0.05.
0 0.2 0.4 0.6 0.8 1
Mean Annual Bromide (mg/L)
Sample Site
Mean Annual Sulfate (mg/L)
Sample Site
59
3.1.6.2. High Flow Conditions
There were no significant differences in high flow fluoride concentrations among the creeks sampled. Concentrations ranged from 0.23 mg/L in Carter 1 to 0.68 mg/L in Carter 4 (Table 17).
Chloride concentrations during high flow were higher in Carter 5 than in Briar 2, Burton 5 and the upper Carter sites (Figure 28). Wolfpen was next highest, with significantly higher values than Briar 2, Burton 5 and Carter 3. Carter 4 was higher than Burton 5.
High flow bromide concentrations were significantly higher in Wolfpen than in Burton 3 and Burton 4; both Briar sites; Carter 1, 2, and 4; and Hudson (Figure 29).
Sulfate high flow concentrations were significantly higher in Bee Creek than in any of the other sites except Burton 3 and Wolfpen (Figure 30).
Table 17. Mean annual fluoride concentrations during high flow. Equivalent letters signify no significant difference at the p ≤ 0.05 level.
Site Name N Mean Std Dev Std Error Minimum Maximum
Bee 10 a0.31 0.35 0.11 0.1 1.27
Briar 1 10 a0.43 0.55 0.17 0.06 1.61
Briar 2 10 a0.32 0.39 0.12 0.05 1.21
Burton 1 10 a0.43 0.55 0.18 0.1 1.74
Burton 2 10 a0.50 0.71 0.22 0.1 2.04
Burton 3 10 a0.45 0.56 0.18 0.07 1.68
Burton 4 10 a0.51 0.60 0.19 0.06 1.71
Burton 5 10 a0.43 0.53 0.17 0.11 1.44
Carter 1 9 a0.23 0.35 0.12 0.06 1.17
Carter 2 9 a0.39 0.52 0.17 0.03 1.55
Carter 3 9 a0.38 0.59 0.20 0.06 1.74
Carter 4 10 a0.68 0.32 0.10 0.1 1.01
Carter 5 9 a0.65 0.49 0.16 0.21 1.82
Hudson 10 a0.54 0.49 0.15 0.07 1.73
Wolfpen 9 a0.54 0.61 0.20 0.17 2.11
Figure 28. Mean annual chloride concentrations during high flow conditions. Error bars are standard error of the mean. Different letters signify a significant difference between mean concentrations.
Figure 29. Mean annual bromide concentrations during high flow conditions. Error bars are standard error of the mean. Different letters signify a significant difference between mean concentrations.
Chloride at High Flow (mg/L)
Sample Site
Bromide at High Flow (mg/L)
Sample Site
61
Figure 30. Mean annual sulfate concentrations during high flow conditions. Error bars are standard error of the mean. Different letters signify a significant difference between mean concentrations.
3.1.6.3. All Flow Conditions
When combining high and low flow data, chloride concentrations in all flow were greater in Carter 5, Bee and Wolfpen than in all the sites except for Burton 3 and Carter 4 (Figure 31).
Carter 4 was significantly higher than both Briars; Burton 2, 4 and 5; Hudson; and the upper Carter sites. Burton 3 was higher than Briar 2, Carter 1 and Carter 3.
Fluoride concentrations were significantly higher in Carter 4 and 5 than the other sites, with exception of Hudson and Wolfpen, reflecting the irrigation water footprint (Figure 32).
Mean annual bromide concentrations remained higher in Wolfpen than in any other creek sampled. Burton 2 was also significantly higher than Briar 2, but no other significant differences were discovered (Figure 33).
0 20 40 60 80 100
Sulfate at High Flow (mg/L)
Sample Site
All flow sulfate concentrations were statistically higher in Bee Creek than in any other site besides Wolfpen (Figure 34). Burton 3 and Hudson were not significantly different from Wolfpen, but were higher than the Briar sites, the upper Carter sites and Burton 4. Burton 5 and Carter 5 were also higher than the Briar sites, Burton 4, Carter 1 and Carter 3, while Carter 4 was only higher than Briar 2 and Carter 3. Interestingly, the sites downstream of the wastewater treatment plant were not significantly different from most of the Burton sites, Carter 2 or Hudson, suggesting that sulfate may be an irrigation-water characteristic but is not significantly elevated by wastewater treatment in this watershed.
Figure 31. Mean annual chloride concentrations during all flow conditions. Error bars are standard error of the mean. Different letters signify a significant difference between mean concentrations.
Mean Annual Chloride (mg/L)
Sample Site
63
Figure 32. Mean annual fluoride concentrations during all flow conditions. Error bars are standard error of the mean. Different letters signify a significant difference between mean concentrations.
Figure 33. Mean annual bromide concentrations during all flow conditions. Error bars are standard error of the mean. Different letters signify a significant difference between mean concentrations.
Mean Annual Fluoride (mg/L)
Sample Site
Mean Annual Bromide (mg/L)
Sample Site
Figure 34. Mean annual sulfate concentrations during all flow conditions. Error bars are standard error of the mean. Different letters signify a significant difference between mean concentrations.
3.1.6.4. Seasonal Variation
Fluoride concentrations in summer showed significantly higher levels in Carter 4 and 5 than in the upper Carter sites (1-3) and Briar 2. Hudson Creek was also higher than Carter 3 in summer. In the fall, Carter 4, Carter 5 and Hudson were significantly higher than all other sites except Wolfpen, which was in turn higher than the upper Carter sites, both Briar sites, and Burton 2, 3, 4 and 5. Winter fluoride concentrations were higher in Carter 4 and 5 than in all others except Hudson and Wolfpen, with Wolfpen showing higher concentrations than Carter 1, Carter 3 and Briar 2, and Hudson only higher than Carter 3. There were no significant
differences in spring, but Carter 4 and 5 maintained the highest mean values.
Chloride concentrations for the summer sample times showed no significant difference. In the fall, however, there were several differences, with Wolfpen containing higher concentrations
0 20 40 60 80 100
Mean Annual Sulfate (mg/L)
Sample Site
65
than Hudson, Briar 1, Briar 2, Burton 2, Burton 5, Carter 1 and Carter 3. Carter 5 was also higher than Carter 1, Carter 3 and Briar 2, while Bee Creek was higher than Briar 2 and Carter 3, and Carter 4 was higher than Carter 3. In winter, Wolfpen, Burton 3 and Carter 5 were higher than all the other creeks except for Bee Creek and Carter 4. These two were higher than Briar 2 and Carter 3. Spring chloride values were greater in Wolfpen than in Burton 5 or Briar 2.
Wolfpen maintained higher bromide concentrations than any other site throughout summer, fall and winter seasons, with mean values more than twice as high as the next highest site. In spring, Wolfpen remained significantly higher than Burton 4, Carter 1 and the Briar sites, but was not significantly different from the other creeks sampled.
Summer sulfate concentrations were higher in Bee Creek than in all the other creeks except for Burton 5, Hudson and Wolfpen. Burton 5 and Hudson were higher than Burton 4, Carter 3 and Briar 2, while Wolfpen was only higher than Carter 3 and Briar 2. In the fall, Wolfpen and Bee were higher than Carter 1, Carter 3, Burton 2 and the Briar sites, while Wolfpen alone was also higher than Burton 1, Burton 2 and Carter 2. In winter, Bee was higher than all the other sites except Wolfpen and Burton 3. Wolfpen winter concentrations were higher than Carter 1, Carter 3 and the Briar sites; Burton 3 was also higher than Briar 2. Bee Creek was also higher in the spring than Burton 1, 2, 4, and 5; the upper Carter sites; and the Briar sites.
3.2. Geographical Distribution of E. coli in Carters Creek 3.2.1. E. coli Accumulation with River Miles
Counts of E. coli were found to be greatest in the Burton Creek subcatchments in both dry and wet conditions, as shown in Figures 35 and 36 (please note different E. coli scales). In dry conditions, Burton 4 has conspicuously high E. coli counts which likely become diluted, killed or settled out of suspension by the time the stream reaches Burton 2, and again before Burton 1.
In wet conditions the nested Burton sample sites are much more clustered together, indicative of the greater hydrologic connectivity and the flush of E. coli that reaches much farther downstream than in dry conditions. Also of note is the diluting effect of WWTP effluent on E. coli counts, especially during wet weather. Although there is no significant difference among any of the creeks during high flow, the high flow geometric mean for Carter 4 (downstream of a WWTP) was lower than that of any of the measured sites immediately upstream and less than half of the Burton 1 geometric mean.